Viviparus sphaeridius Bourguignat 1880

(Figs. 2-5)

Materials examined: 3 adult females from Danube near vill. Marten 14.05.2009 Georgiev leg.; 7 empty shells from Brashlen near Marten. June 2008 Georgiev leg.

Redescription: Shell oval conical, thick and yellowish brown (Fig 3B) with three brownish bands (Fig. 3E), not visible in the adults. The 5-6 whorls are slightly convex with a flat suture and an acute apex (Fig. 3D, 3E). The body whorl is very bulbous, the umbilicus is scarcely visible. The first two whorls are very small in height, the others are regularly fast growing. Spire height about a fifth of shell height. Shell height 24-28 mm, width 18-20 mm.

Differentiating features: V. sphaeridius belongs to the smaller Viviparus spp. of Europe, together with V. viparus and V. hellenicus (Fig. 4). Independent of the shell height it can be distinguished by the acute apex from V. viviparus which has a blunt apex. It differs from V. hellenicus in the form of the body whorl, which is canted in this species while the body whorl in V. sphaeridius is rounded. From V. acerosus, which also occurs in this region it can be distinguished by the first whorls, which are more flattened in V. sphaeridius and less convex than in V. acerosus. In addition the spire is less higher than in V. acerosus.

Associated species: Theodoxus danubialis (C. Pfeiffer, 1828), Bithynia danubialis Glöer & Georgiev 2012, Bithynia tentaculata (Linnaeus, 1758), Lithoglyphus naticoides (C. Pfeiffer, 1828), and Esperiana daudebartii (Prevost, 1821).

Habitat and ecology: V. sphaeridius was collected from the littoral zone of the Danube from sandy bottom with patches of aquatic macrophytes.

Distribution: Rivers and lakes of the basins of Danube, Dnieper and Dniester rivers (Anistratenko 1998b; Starobogatov et al. 2004; cited after Kantor et al. 2009).